The Irregular Terrain Model (ITM) estimates radio propagation losses for frequencies between 20 MHz and 20 GHz as a function of distance and the variability of the signal in time and space. It is an improved version of the Longley-Rice Model , which gives an algorithm developed for computer applications. The model is based on electromagnetic theory and signal loss variability expressions derived from extensive sets of measurements . The ITM is applicable to point-to-area calculations. The "point" is where a broadcast station or a base station for mobile service may be located and "area" refers to locations of broadcast receivers or mobile stations. The ITM algorithm works in two modes: 1) area prediction mode - used when an exact terrain description is not available, and 2) point-to-point prediction mode - when terrain profile between the terminals is available.